Without its own route to London, the Midland Railway relied upon a junction at Rugby with the London and Birmingham Railway line for access to the capital at London Euston. By the 1850s the junction at Rugby had become severely congested. The Midland Railway employed Thomas Brassey to construct a new route from Leicester to Hitchin via Kettering, Wellingborough and Bedford.[5] giving access to London via the Great Northern Railway from Hitchin. The Crimean War resulted in a shortage of labour and finance, and only £900,000 (equivalent to £77,430,000 in 2015)[6] was available for the construction, approximately £15,000 for each mile.[7] To reduce construction costs the railway followed natural contours, resulting in many curves and gradients. Seven bridges and one tunnel were required, with 60ft cuttings at Desborough and Sharnbrook. There are also major summits at Kibworth, Desbrough and at Sharnbrook where a 1 in 119 gradient from the south over 3 miles takes the line to 340 feet (100 m) above sea level. This route opened for coal traffic on 15 April 1857, goods on 4 May and passengers on 8 May[8] and the section between Leicester and Bedford is still part of the Midland Main Line.

While this took some of the pressure off the route through Rugby, the GNR insisted that passengers for London alight at Hitchin, buying tickets in the short time available, to catch a GNR train to finish their journey. James Allport arranged a seven-year deal with the GN to run into Kings Cross for a guaranteed £20,000 a year (equivalent to £1,720,000 in 2015).[6] Through services to London were introduced in February 1858.[9]

This line met with similar capacity problems at Hitchin as the former route via Rugby, so a new line was constructed from Bedford via Luton to St Pancras[10] which opened on 1 October 1868.[7] The construction of the London extension cost £9,000,000[11] (equivalent to £730,290,000 in 2015).[6]

In 1977 the Parliamentary Select Committee on Nationalised Industries recommended considering electrification of more of Britain's rail network, and by 1979 BR presented a range of options that included electrifying the Midland Main Line from London to Yorkshire by 2000.[14] By 1983 the line had been electrified from Moorgate to Bedford, but proposals to continue electrification to Nottingham and Sheffield were not implemented.

The introduction of the High Speed Train (HST) in May 1983, following the Leicester area resignalling, brought about an increase of the ruling line speed on the fast lines from 90 miles per hour (140 km/h) to 110 miles per hour (180 km/h).

Between 2001 and 2003 the line between Derby and Sheffield was upgraded from 100 miles per hour (160 km/h) to 110 miles per hour (180 km/h) as part of Operation Princess, the Virgin-funded CrossCountry route upgrade.

Most recently 125 miles per hour (201 km/h) running has been introduced on extended stretches. Improved signalling, increased number of tracks and the revival of proposals to extend electrification from Bedford to Sheffield are underway. Much of this £70 million upgrade, including some line-speed increases, came online on 9 December 2013[16] (see below).

Network Rail published a Route Utilisation Strategy for freight in 2007;[17] over the coming years a cross-country freight route will be developed enhancing the Birmingham to Peterborough Line, increasing capacity through Leicester, and remodelling Syston and Wigston junctions.

Bridges over the Midland Main Line have been replaced to allow greater clearances for electrification and larger rolling stock. Before (top) and after (bottom) the 2014 upgrade.

Traffic levels on the Midland Main Line are rising faster than the national average, with continued increases predicted. In 2006 the Strategic Rail Authority produced a Route Utilisation Strategy for the Midland Main Line to propose ways of meeting this demand;[18]Network Rail started a new study in February 2008 and this was published in February 2010.[19][20][21][22] After electrification, the North Northamptonshire towns (Wellingborough, Kettering and Corby) are planned to have an additional 'Outer Suburban service' into London St. Pancras, similar to the London Midland's Crewe – London Euston services to cater for the growing commuter market. North Northamptonshire is a major growth area, with over 7,400 new homes planned to be built in Wellingborough[23] and 5,500 new homes planned for Kettering.[24] The service will be operated by new Class 387s.[25]

Lengthening of platforms at Wellingborough, Kettering, Market Harborough, Loughborough, Long Eaton and Beeston stations as well as work related to the Thameslink Programme (see below).

Realignment of the track and construction of new platforms to increase the permissible speed through Market Harborough station from 60 mph to 85 mph saving between 30 – 60 seconds.

Electrification (below)

Re-doubling the Kettering to Oakham Line between Kettering North Junction and Corby as well as re-signalling to Syston Junction via Oakham. This will allow a half hourly London to Corby passenger service (from an infrastructure perspective) from December 2017 possibly using Class 387s, and will create additional paths for rail freight.[30][31]

Diesel Class 222 Meridian trains will no longer be needed for most services after electrification

On 16 July 2012, the Department for Transport announced plans to reconfigure the existing electrified section and to electrify most of the line by 2020 at an expected cost of £800 million.[32] In January 2013 Network Rail expected the electrification to cost £500 million and be undertaken in stages during Control Period 5 (April 2014 – March 2019),[33] with Bedford to Corby section electrified by 2017, Kettering to Derby and Nottingham by 2019 and Derby to Sheffield by 2020.[34] Those plan[citation needed] did not include electrification of Nottingham to Clay Cross via Alfreton, nor Corby to Syston via Oakham.

In the Route Utilisation Strategy, Network Rail recommended the Class 801 in 10 car formations for the InterCity services,[38] two 775 metres (848 yd) freight loops south of Bedford and between Kettering and Leicester for longer and heavier freight services, additional infrastructure to accommodate additional freight and passenger train paths and also recommended an additional stop at Kettering for the semi-fast London-Sheffield service.

The Thameslink Programme has seen the platforms at all stations south of Bedford apart from St Pancras, Kentish Town, Cricklewood, Hendon and Luton Airport Parkway, which were already long enough, be lengthened to 12-car capabilities. West Hampstead Thameslink has had a new footbridge installed and a new station building constructed. In September 2014 the current Thameslink Great Northern franchise was awarded and trains on this route are currently operated by Thameslink. In 2018 the Thameslink network will additionally be expanded with some Southern services being merged into it.

In 1868 the term was used to describe the Midland Railway main route from North to South through Sheffield[51] and also on routes to Manchester, Leeds and Carlisle.

Under British Rail the term was used to define the route between St Pancras and Sheffield, but in more recent times, Network Rail has restricted it in its description of Route 19[2] to the lines between St. Pancras and Chesterfield.

The principal operator is East Midlands Trains, which operates 5 InterCity trains every hour from London St Pancras with two trains per hour to Nottingham and Sheffield and one train per hour to Corby. EMT use Class 222 Meridian trains in various carriage formations for most of its InterCity services. Traditional 8 coach HSTs are used for its Nottingham fast service as well morning/evening Leeds services.

CrossCountry runs half-hourly services between Derby and Sheffield on its route between the South West and North East, and hourly services from Nottingham to Birmingham and Cardiff. Northern runs an hourly service to Leeds from Nottingham via Alferton and Barnsley.

The cities, towns and villages currently served by the MML are listed below. Stations in bold have a high usage. This table includes the historical extensions to Manchester (where it linked to the West Coast Main Line) and Carlisle (via Leeds where it meets with the 'modern' East Coast Main Line).

Network Rail groups all lines in the East Midlands and the route north as far as Chesterfield and south to London as route 19. The actual line extends beyond this into routes 10 and 11.

This line was closed in the 1960s between Matlock and Buxton, severing an important link between Manchester and the East Midlands, which has never been satisfactorily replaced by any mode of transport. A section of the route remains in the hands of the Peak Rail preservation group, operating between Matlock and Rowsley to the north.

For marketing and franchising, this is no longer considered part of the Midland Main Line: see Settle-Carlisle Railway.

A geographical representation of the aborted Midland Main Line diversion through the West Riding, which would have put Bradford on a through line and provided a direct connection to Scotland. (Existing lines shown in black and the diversion in red).

The first part of the Midland's West Riding extension from the main line at Royston (Yorks.) to Dewsbury was opened before the war. However, the second part of the extension was not completed. This involved a viaduct at Dewsbury over the River Calder, a tunnel under Dewsbury Moor and a new approach railway into Bradford from the south at a lower level than the existing railway (a good part of which was to be in tunnel) leading into Bradford Midland (or Bradford Forster Square) station.

The 500 yards (460 m) gap between the stations at Bradford still exists. Closing it today would also need to take into account the different levels between the two Bradford stations, a task made easier in the days of electric rather than steam traction, allowing for steeper gradients than possible at the time of the Midland's proposed extension.

Two impressive viaducts remain on the completed part of the line between Royston Junction and Dewsbury as a testament to the Midland's ambition to complete a third direct Anglo-Scottish route. The line served two goods stations and provided a route for occasional express passenger trains before its eventual closure in 1968.

The failure to complete this section ended the Midland's hopes of being a serious competitor on routes to Scotland and finally put beyond all doubt that Leeds, not Bradford, would be the West Riding's principal city. Midland trains to Scotland therefore continued to call at Leeds before travelling along the Aire Valley to the Settle and Carlisle. From Carlisle they then travelled onwards via either the Glasgow and South Western or Waverley route. In days gone by the line enjoyed named expresses such as the Thames-Clyde Express and The Waverley.

As with most railway lines in Britain, the route used to serve far more stations than it currently does (and consequently passes close to settlements that it no longer serves). Places that the current main line used to serve include

^"Midlands line 'to be electrified'". BBC News Online. 14 July 2012. Retrieved 14 July 2012. A £500m scheme … Transport Secretary Justine Greening is set to outline plans to complete the electrification of the route from Sheffield to London on Monday.

^Odell, Mark; Parker, George (13 July 2012). "Osborne backs £10bn rail plan". Financial Times. Retrieved 14 July 2012. announcement, expected on Monday, is likely to include a £530m plan to complete electrification of the Midland mainline between Bedford and Sheffield